A program of research is proposed which explores membrane structure by employing highly specific chemical probes at selective membrane components. Two specific approaches are utilized in this investigation: 1) It is proposed that photo-affinity labeling reagents be synthesized for membrane binding sites, i.e. hormonal receptor components, transport binding components, and mitochondrial uncoupler and inhibitor binding components. The synthesis of several adenine nucleotide photo-affinity analogues is proposed for labeling binding sites in multi-subunit ATPases and soluble enzymes. Utilization of these labels is directed towards isolation and characterization of the respective membrane components from those systems in which labeling specificity can be attained. Studies with photo-affinity analogues of PGF1 alpha, ADP and transportable amino acids which we have already synthesized will be extended. 2) The second approach concerns isotopic probes at, and selective chemical modification of, the membrane-bound and purified Na, K ions-ATPase. The aims are to use 18O and group specific reagents to investigate the energy-coupling reactions of the ATPase. The proposed investigation should broaden our understanding of how biologically important molecules interact with membrane components and yield some of the details of membrane structure necessary for membrane function. Likewise, probes at energy-coupling reactions of the Na, K ions-ATPase could yield pertinent insights into the mechanism of the enzyme as well as the mechanism of transport.